1. Field of the Invention
The present invention relates to a valve, and more particularly to a valve for permanent venous cannulae or for catheter insertion means.
2. Description of Related Art
To insert a venous catheter into a blood vessel, the vessel is first punctured with a permanent venous cannula. Such permanent venous cannulae typically consist of a steel cannula and plastic cannula slipped thereon. As soon as the puncture is made, the steel cannula is pulled out of the plastic cannula. The venous catheter can be inserted through the plastic cannula remaining in the vessel. It is also possible to leave the plastic cannula in the blood vessel for use as a short permanent catheter.
After the steel cannula has been pulled out of the plastic cannula, following a vessel puncture, blood may flow through the plastic cannula. Air may also enter the patient's body and air embolism may occur, if by an elevation of the thorax of the patient or by extreme desiccation of the patient the central venous pressure is negative.
In an attempt to avoid the risk of both an "air embolism" and a "blood contamination of the physician", German Patent 28 17 102 C2 discloses a valve integrated into the connection piece of a permanent venous cannula, which valve can only be opened in the direction toward the patient by mechanical action. A slotted Latex-disc serves as a valve body. In the delivery condition of the permanent venous cannula, the steel cannula is lead through the disc. After the puncture and the subsequent withdrawal of the steel cannula, the disc shuts itself due to its resilience. After that, a Luer connector can be set on the connection piece, which pushes open the disc with its conic pipe socket, so that the disc opens for the insertion of a venous catheter.
This known valve poses difficulties in storage, since it is stored with the steel cannula inserted through the disc. In the course of time, the elastomeric material of the disc loses its resilience, so that there is a danger that the valve will fail to close after a long storage. Thus, that part of the steel cannula that is enclosed by the elastic disc is made thinner than the rest of the cannula. Thus, the valve is spread open only negligibly during its storage. However, there is a danger that tissue particles and thrombi of the patient may settle at the constriction of the steel cannula, which could obstruct the constriction.
It is an object of the invention to provide a valve in which the valve shuts tightly, after the steel cannula has been pulled out and even after having been kept open for a long time.